Silicon carbide (SiC) is increasingly recognized as an effective semiconductor material for electronic devices. SiC possesses a number of properties that make it particularly attractive for applications requiring devices to operate at high temperature, power and/or frequency. SiC exhibits highly efficient heat transfer and is capable of withstanding high electric fields.
It has been demonstrated that hot-wall chemical vapor deposition (CVD) reactors can provide epitaxial layers of SiC with morphology and doping superior to cold-wall systems. See, for example, U.S. Pat. No. 5,695,567 to Kordina et al., the disclosure of which is hereby incorporated herein by reference. In certain processes, such as epitaxial growth processes, management of the thermal profile in the vicinity of the substrate may be of great importance. Temperature gradients may dramatically influence many growth parameters and the qualities of the resulting layers. Where the substrate is disposed on a platter (e.g., for rotation) separate from a surrounding susceptor and induction heating is employed, the platter may be significantly cooler than the internal surfaces of the susceptor. More particularly, the susceptor may be directly heated by an RF field while the platter is only or predominantly heated by thermal conduction and radiation from the susceptor. The substrate may be cooler even than the platter. As a result, a substantial thermal gradient may be manifested between the substrate growth surface and the internal surfaces of the susceptor. The thermal gradient may be further exacerbated by the cooling effect of a process gas flow through the susceptor.
The aforementioned temperature gradient may present a number of problems. Such problems may include the formation of loose deposits (e.g., SiC) on the hot susceptor wall. Such deposits may fall onto the substrate and be incorporated into the epilayers. Moreover, temperature gradients may cause difficulty in controlling material properties as a result of non-controllable variations in the temperature gradient and the narrowing of process windows.
The foregoing problems may also be presented in other types of processes such as other types of deposition processes and annealing processes.